CN113545125A

CN113545125A - Apparatus and method for controlling access to a cell

Info

Publication number: CN113545125A
Application number: CN202080019402.XA
Authority: CN
Inventors: 李贤龙
Original assignee: SK Telecom Co Ltd
Current assignee: SK Telecom Co Ltd
Priority date: 2019-04-25
Filing date: 2020-03-03
Publication date: 2021-10-22
Also published as: WO2020218732A3; KR20200125033A; US20220132592A1; KR102397380B1; KR102283629B1; KR20210095613A; WO2020218732A2

Abstract

The present disclosure provides a new scheme (technique) capable of minimizing a data interruption time occurring at a user equipment side while performing a normal access procedure during an access between the user equipment and a cell (e.g., a target cell) in a MIMO system.

Description

Apparatus and method for controlling access to a cell

Technical Field

The present disclosure claims priority based on korean patent application No.10-2019-0048686, filed on 25/4/2019, the entire contents of which are hereby incorporated by reference for all purposes.

The present disclosure relates to a technique for minimizing a data interruption time on a User Equipment (UE) side when the UE accesses a cell in a communication system using a beamforming technique.

Background

When communication is performed based on a beamforming technique under the condition that both a transmitting apparatus and a receiving apparatus are equipped with a plurality of antennas, there are various techniques in which a gain of transmission capacity can be expected in proportion to the number of transmitting antennas and the number of receiving antennas. A representative technique thereof is a Multiple Input Multiple Output (MIMO) technique.

In a MIMO technology communication system (hereinafter referred to as a "MIMO system"), a transmitting/receiving apparatus communicating based on a beamforming technology transmits (transmits/receives) data through an optimal antenna beam having an optimal signal quality among various directions/forms of antenna beams that can be formed by the transmitting apparatus and the receiving apparatus.

Further, when there is a neighboring cell having higher signal quality measured by a User Equipment (UE) than a source cell due to movement of the UE or the like in a mobile communication system, a handover technique is performed to cause the UE to access a target cell, thereby switching access of the UE from the source cell to the target cell.

To briefly describe the existing handover scheme, when handover of a UE to a target cell is determined based on information reported from the UE, a source cell transmits an RRC connection reconfiguration message for performing an access procedure based on the target cell to the UE.

Upon receiving the RRC connection reconfiguration message, the UE interrupts a data transmission operation based on the source cell and performs an access procedure based on the target cell, starting from a random access procedure attempting to access the target cell.

When the target cell-based access procedure is completed, the UE may perform a data transmission operation based on the target cell.

When the existing handover scheme is applied to the MIMO system, it may take a long time for the target cell to receive a random access preamble (random access procedure start signal) transmitted by the UE through a specific beam of the target cell by performing RX beam scanning for receiving the random access preamble based on a beamforming technique.

However, the existing handover schemes do not consider a large amount of time required for the target cell to receive the random access preamble (random access procedure start signal) of the UE.

Therefore, when the existing handover scheme is applied to the MIMO system, a data interruption time for stopping a data transmission operation from a time when an RRC connection reconfiguration message is received to a time when an access procedure based on a target cell is completed becomes long in the UE.

Disclosure of Invention

Technical problem

The present disclosure is directed to providing a technique capable of minimizing a data interruption time on a UE side while enabling a normal access procedure to be performed when a connection is made between a User Equipment (UE) and a cell (e.g., a target cell) in a MIMO system.

Technical solution

A cell access control device according to an embodiment of the present disclosure may include: a cell check unit configured to identify a second cell to which a User Equipment (UE) accessing a first cell will access based on a measurement report received from the UE; a time determination unit configured to determine a transmission time of a specific message for inducing an attempt to access the second cell; and a message transmitting unit configured to delay transmission of the specific message to the UE and transmit the specific message at the determined transmission time when the specific message is generated.

Specifically, the specific message may be an RRC connection reconfiguration message that, when received by the UE, causes the UE to stop data transmission operation based on the first cell and attempt to access the second cell, thereby performing an access procedure.

Specifically, the measurement report may include information on a specific beam having the best signal quality measured by the UE among a plurality of beams formed in different directions in the second cell, and the time determination unit may be configured to determine the transmission time based on Physical Random Access Channel (PRACH) configuration information identified for the second cell and the information on the specific beam.

In particular, the time determination unit may be configured to: predicting a particular time to receive an attempt from the UE to access the second cell over the particular beam based on the PRACH configuration information and the information about the particular beam; and determining the transmission time based on the predicted specific time.

Specifically, the specific time predicted may be a PRACH slot position to which a resource allocated to the specific beam identified from the PRACH configuration information and a RACH Occasion (RO) previously allocated to the UE are mapped.

In particular, the time determination unit may be configured to: predicting a processing time required to process the specific message after receiving the specific message, and transmitting a message for attempting to access the second cell based on performance information of the UE; and determining a time earlier than the predicted specific time by the processing time as the transmission time.

Specifically, the message transmitting unit may be configured to immediately transmit the specific message regardless of the transmission time when a specific event that the signal quality of the first cell is lower than a threshold is reported from the UE while the specific message is transmitted later.

A cell access control method according to an embodiment of the present disclosure may include: a cell checking step of identifying a second cell to which a User Equipment (UE) accessing a first cell will access, based on a measurement report received from the UE; a time determination step of determining a transmission time of a specific message generated for inducing an attempt to access the second cell based on the measurement report; and a message transmission step of delaying transmission of the specific message to the UE when the specific message is generated, and transmitting the specific message at the determined transmission time.

Specifically, the measurement report may include information on a specific beam having the best signal quality measured by the UE among a plurality of beams formed in different directions in the second cell, and the time determining step may include determining the transmission time based on Physical Random Access Channel (PRACH) configuration information identified for the second cell and the information on the specific beam.

Specifically, the time determining step may include: predicting a particular time to receive an attempt from the UE to access the second cell over the particular beam based on the PRACH configuration information and the information about the particular beam; and determining the transmission time based on the predicted specific time.

Specifically, the time determining step may include: predicting a processing time required to process the specific message after receiving the specific message, and transmitting a message for attempting to access the second cell based on performance information of the UE; and determining a time earlier than the predicted specific time by the processing time as the transmission time.

Specifically, the message transmitting step may include immediately transmitting the specific message regardless of the transmission time when a specific event that the signal quality of the first cell is lower than a threshold is reported from the UE while the specific message is transmitted later.

Advantageous effects

According to the embodiments of the present disclosure, it is possible to provide an effect that a data interruption time on the UE side can be minimized while enabling a normal access procedure to be performed when a connection is made between a UE and a cell (e.g., a target cell) in a MIMO system.

Drawings

Fig. 1 is a diagram illustrating an example of a communication system environment to which the present disclosure is applied.

Fig. 2 is a flowchart illustrating an embodiment in which an existing handover scheme is applied to a communication system to which the present disclosure is applied.

Fig. 3 is a diagram illustrating a configuration of a cell access control apparatus according to an embodiment of the present disclosure.

Fig. 4 is a flowchart illustrating an example of applying a cell access control method (scheme) according to an embodiment of the present disclosure.

Fig. 5 is a flowchart illustrating an example of applying a cell access control method (scheme) according to another embodiment of the present disclosure.

Fig. 6 is a control flow diagram illustrating a cell access control method according to an embodiment of the present disclosure.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

Fig. 1 illustrates a communication system environment to which the present disclosure is applied.

The present disclosure is based on a transmitting apparatus equipped with a plurality of antennas and a receiving apparatus equipped with a plurality of antennas, and is based on a multiple-input multiple-output (MIMO) technique for performing communication based on a beamforming technique.

In a MIMO technology communication system (hereinafter referred to as a "MIMO system"), the maximum transmission capacity gain is a diversity gain and a multiplexing gain by beamforming.

For this purpose, beamforming techniques used in the MIMO system may be classified into digital beamforming, analog beamforming, hybrid beamforming, and the like.

In the case of digital beamforming, the number of formable beams is determined by the number of RF chains.

The plurality of beams formed by digital beamforming may be used as a means for increasing signal quality (signal to interference and noise ratio, SINR) by improving diversity of the receiving end, and may also be used for multiplexing by separating the plurality of receiving ends into different beams to respectively receive different signals.

The plurality of beams formed through analog beamforming may be used only as a means for increasing signal quality (SINR) by improving diversity at a receiving end.

The disadvantage of the digital beamforming technique in which the installation cost increases due to the need for as many RF chains as the number of antennas and the disadvantage of the analog beamforming technique in which the performance gain is limited, among others, results in the use of a hybrid beamforming technique in the form of a combination of the two beamforming techniques in a MIMO system.

In particular, a 5G mobile communication network using a high frequency band (hereinafter, referred to as a "5G MIMO system") uses an analog beamforming technique (single or hybrid) due to frequency characteristics of high linearity.

In the MIMO system, a transmitting/receiving apparatus that communicates based on a beamforming technique transmits (transmits/receives) data through an optimal beam having an optimal signal quality among antenna beams of various directions/forms that can be formed by the transmitting apparatus and antenna beams of various directions/forms that can be formed by the receiving apparatus.

Further, in the mobile communication system, if there is a neighboring cell having a signal quality measured by a User Equipment (UE) higher than that of a source cell due to movement of the UE or the like, a handover technique of handing over a connection of the UE from the source cell to a target cell by causing the UE to access the target cell is used.

Fig. 1 illustrates handover due to movement of a UE in a MIMO system.

Fig. 1 illustrates, as an exemplary embodiment only, a base station form in which a base station module (e.g., a central unit) and a wireless module (e.g., a distributed unit) are separated and installed at a long distance (hereinafter, referred to as a separation type base station) among various forms of base stations.

If the UE1, which stays in the cell of the radio module 10 (i.e., DU 10) and uses the data service through the base station module 100 (i.e., CU 100) based on the cell of the DU 10, moves to the cell of the DU20, there may be a time when the signal quality measured for the cell of the DU20 becomes better than the signal quality measured for the cell of the DU 10, which is the source cell.

In this case, CU 100 may cause UE1 to access the target cell (i.e., the cell of DU 20) through a series of signaling operations for handover, thereby handing over the connection of UE1 from the source cell to the target cell.

Fig. 2 shows an example of applying an existing handover scheme to a MIMO communication system.

To briefly describe the existing handover scheme with reference to fig. 2, the UE may use a data service through the CU based on a source cell (i.e., a cell of a source DU).

Further, each DU performs TX beam scanning for transmitting a specific signal (e.g., SSB, CSI-RS, etc.) including a beam identifier of each of a plurality of beams formed by the DU based on a beamforming technique in the MIMO communication system.

Fig. 2 illustrates a case (r) where each DU (source DU or target DU) performs TX beam scanning for transmitting an SSB signal (SSB #1, #2, … # n) including a beam identifier (e.g., an SSB index) of each of a plurality of beams formed by the DU.

In addition, the UE measures a received specific signal (e.g., SSB, CSI-RS, etc.) and transmits a measurement report MR (c) for reporting signal qualities (e.g., SINR, RSRP, PSRQ, etc.) of respective beams of neighboring cells.

In this case, fig. 2 shows a case where the signal quality measured for a specific beam in which the signal SSB # i of the target DU is transmitted is the best as a result of the UE measuring the signal quality of each beam of the neighboring cells (source DU and target DU).

The CU receives a measurement report MR of the UE through the source DU, and determines handover so that a corresponding neighbor cell becomes a target cell (target DU) of the UE if there is a neighbor cell having a signal quality equal to or higher than the signal quality of the source DU by a certain value based on the measurement report. In addition, the CU can perform the handover preparation procedure (c) by signaling (target cell AU setup request and target cell AU setup response) with the target DU.

After performing the handover preparation procedure, the CU transmits to the UE an RRC connection reconfiguration message for performing an access procedure based on the target cell, i.e., the target DU (r).

Furthermore, the CU allocates resources (RACH occasion, RO) capable of transmitting a random access preamble for each UE in a radio resource (physical random access channel, PRACH) designated to perform RX beam scanning in a Physical Random Access Channel (PRACH) period predefined for the respective DU connected thereto.

Accordingly, the UE receiving the RRC connection reconfiguration message stops the data transmission operation based on the source cell (i.e., source DU) and transmits a random access preamble at the RO allocated thereto (sixth) to start a random access procedure to attempt to access the target DU, thereby performing the access procedure based on the target DU.

Further, in the MIMO communication system, each DU performs RX beam scanning based on a beamforming technique to receive a random access preamble.

Accordingly, as shown in fig. 2, a target DU, which is a target cell for a current handover, may allocate a plurality of beams to each cell resource in each PRACH slot according to a beam mapping rule based on a Physical Random Access Channel (PRACH) configuration defined therein, and may perform RX beam scanning in units of PRACH slots (PRACH #1, #2, … # n).

After receiving the RRC connection reconfiguration message, the UE transmits a random access preamble (random access procedure start signal) through a specific beam (e.g., a beam of SSB # i) of the target DU, which is measured to have the best signal quality, in the RO allocated thereto.

Accordingly, the target DU may receive a random access preamble in a PRACH slot (e.g., PRACH # j) mapped to the RO of the UE while performing RX beam scanning in units of PRACH slots (PRACH #1, #2, … # n), and may perform a random access procedure (c) through a random access response thereto and a series of signaling operations.

Thereafter, the target DU-based access procedure may be performed through a series of signaling operations among the UE, the target DU and the CU, and if the UE transmits an RRC reconfiguration complete message to the CU through the target DU, the access procedure may be completed such that the UE can use a data service through the CU based on the target cell (i.e., the cell of the target DU).

That is, on the UE side, there is a data interruption time (c) in which a data transmission operation is interrupted from when the RRC connection reconfiguration message is received to when the target cell-based access procedure is completed by transmitting the RRC reconfiguration complete message.

As described above, the target DU, which is the target cell for handover, takes a long time to receive the random access preamble (random access procedure start signal) transmitted by the UE while performing RX beam scanning.

In particular, in the case of a 5G MIMO system using analog beamforming technology (single or hybrid), the RACH period ((r)) may be longer, which lengthens the time taken to receive a random access preamble (random access procedure start signal) transmitted from the UE.

In addition, as seen in fig. 2, the data interruption time is the sum of the time between the UE receiving the RRC connection reconfiguration message and transmitting the RRC reconfiguration complete message and the time 2 α due to the delay (α) between the DU and the CU.

In this case, since the delay (α) between the DU and the CU is negligible, the data interruption time in the UE may be defined as the time between the UE receiving the RRC connection reconfiguration message and transmitting the RRC reconfiguration complete message.

However, the existing handover schemes do not consider a large amount of time required for the target cell to receive the random access preamble (random access procedure start signal) of the UE, so that a data interruption time for stopping a data transmission operation in the UE may be extended.

Accordingly, the present disclosure proposes a new technical solution (hereinafter, referred to as a cell access control scheme) capable of minimizing a data interruption time on a UE side while enabling a normal access procedure to be performed when a connection is made between a UE and a cell (e.g., a target cell) in a MIMO system.

In particular, the new cell access control scheme proposed in the present disclosure may be implemented by a cell access control apparatus described below.

Before specifically describing it, the cell access control apparatus of the present disclosure may be implemented in a base station, and more particularly, in the case of a split-type base station, may be implemented in a radio module (e.g., DU) or a base station module (e.g., CU), or may be implemented such that the functions of the cell access control apparatus are allocated to the radio module (e.g., DU) and the base station module (e.g., CU).

Fig. 3 illustrates a configuration of a cell access control apparatus according to an embodiment of the present disclosure.

As shown in fig. 3, the cell access control apparatus 200 according to an embodiment of the present disclosure may include a cell checking unit 210, a time determining unit 220, and a message transmitting unit 230.

All or at least some of the elements of the cell access control apparatus 200 may be implemented in the form of hardware modules, software modules or a combination of hardware and software modules.

Here, a software module may be understood as instructions executed by, for example, a processor controlling operations in the cell access control apparatus 200, and the instructions may be installed to a memory in the cell access control apparatus 200.

As a result, the cell access control apparatus 200 according to an embodiment of the present disclosure can implement the new cell access control scheme proposed in the present disclosure through the above-described configuration.

Hereinafter, each element in the cell access control apparatus 200 for implementing the scheme of the present disclosure will be described in more detail.

The cell checking unit 210 may identify a second cell to be accessed by the UE having accessed the first cell based on the measurement report received from the UE.

The new cell access control scheme proposed in the present disclosure may be applicable to a dual connection technology supporting simultaneous connection to two or more cells as well as the above-described handover technology.

Accordingly, the cell checking unit 210 may identify a second cell (i.e., a target cell) to be accessed by a UE having accessed a first cell that is a source cell, based on a measurement report received from the UE, assuming a handover technique.

Alternatively, in a case where a dual connection technology is assumed, the cell checking unit 210 may identify a second cell (i.e., a secondary cell) to be accessed by a UE that has accessed a first cell that is a primary cell, based on a measurement report received from the UE.

In addition, the new cell access control scheme proposed in the present disclosure may be applicable to both independent and dependent network structures.

However, hereinafter, for convenience of description, description will be made based on application of the handover technique in the same manner as the above description.

In the MIMO communication system, each DU may perform TX beam scanning for transmitting a specific signal (e.g., SSB, CSI-RS, etc.) including a beam identifier of each of a plurality of beams formed by the DU based on a beamforming technique.

In fig. 1, each of the

DUs

10 and 20 performs TX beam scanning for transmitting an SSB signal (SSB #1, #2, … #6) including a beam identifier (e.g., SSB index) of each of a plurality of beams formed by the DU.

UE1 measures respective specific signals (e.g., SSBs, CSI-RSs, etc.) received from the neighboring cells and transmits a measurement report MR for reporting signal qualities (e.g., SINR, RSRP, PSRQ, etc.) of respective beams of the neighboring cells.

CU 100 receives a measurement report MR of UE1 through a source DU (e.g., a cell of DU 10), and determines handover so that the corresponding neighbor cell becomes a target cell of UE1 if there is a neighbor cell having a signal quality equal to or higher than the signal quality of DU 10 (a3 event) based on the measurement report MR.

That is, as described above, the cell check unit 210 may identify a target cell, for example, a cell of the DU20 to which the CU 100 has determined handover of the UE 1.

The time determination unit 220 performs the function of determining the transmission time based on the UE1 measurement report MR for a specific message for inducing an attempt to access the second cell, i.e., the target cell (e.g., the cell of the DU 20).

Here, the specific message may be an RRC connection reconfiguration message that, when received by the UE1, causes the UE to stop a data transmission operation based on the first cell (e.g., source cell) and attempt to access the second cell (e.g., target cell) to perform an access procedure.

More specifically, if handover to the target cell of the UE1 (e.g., the cell of the DU 20) is determined as described above, the CU 100 generates an RRC connection reconfiguration message enabling an attempt to access the target cell (e.g., the DU 20) to perform an access procedure.

The time determination unit 220 determines the transmission time of the RRC connection reconfiguration message for UE1 generated by the CU 100 as described above based on the measurement report MR of UE 1.

When the above-mentioned specific message is generated, the message transmission unit 230 waits for transmission of the message to the UE1, and then transmits the message to the UE1 at the transmission time determined by the time determination unit 220.

That is, the message transmitting unit 230 waits to transmit the RRC connection reconfiguration message generated by the CU 100 for the UE1 as described above until the transmission time determined by the time determining unit 220, and then transmits the RRC connection reconfiguration message to the UE1 at the transmission time.

Hereinafter, a process of determining a transmission time for the RRC connection reconfiguration message generated by the UE1 will be described in detail.

First, the measurement report MR transmitted from the UE1 includes information on a specific beam having the best signal quality (e.g., SINR, RSRP, PSRQ, etc.) measured by the UE1 among a plurality of beams formed in different directions in a second cell, i.e., a target cell (e.g., the cell of DU 20).

Specifically, the UE1 measures respective specific signals (e.g., SSB, CSI-RS, etc.) received from the neighbor cells, and transmits a measurement report MR for reporting signal quality (e.g., SINR, RSRP, PSRQ, etc.) of each beam of the neighbor cells.

Accordingly, the measurement report MR transmitted from the UE1 includes the signal quality (e.g., SINR, RSRP, PSRQ, etc.) of each beam of the neighboring cell measured by the UE1, and also includes information (e.g., SSB index or SINR/RSRP/PSRQ) about the specific beam measured to have the best signal quality (e.g., SINR, RSRP, PSRQ, etc.).

The time determination unit 220 may determine the transmission time based on Physical Random Access Channel (PRACH) configuration information identified for the second cell (i.e., the target cell of the current handover) and information on a specific beam identified in the measurement report MR of the UE1 (i.e., the specific beam of the target cell).

For this purpose, in the present disclosure, it is necessary for the cell access control apparatus 200 to learn information (e.g., SSB information and PRACH configuration information) of neighboring cells based on the first cell (e.g., DU 10).

According to an embodiment, in the case where all or some of the functions of the cell access control apparatus 200 are implemented in the

DUs

10 and 20, the cell access control apparatus 200 can learn information of neighboring cells, for example, SSB information and PRACH configuration information, based on a first cell (for example, the DU 10) by sharing the SSB information and the PRACH configuration information between the DUs (cells).

According to another embodiment, in the case where the cell access control device 200 is implemented in the CU 100, the CU 100 can learn information of neighboring cells, for example, SSB information and PRACH configuration information, based on a first cell (for example, DU 10) by previously possessing SSB information and PRACH configuration information of the

respective DUs

10 and 20 connected thereto.

More specifically, the time determination unit 220 may predict a specific time to receive an access attempt from the UE1 through a specific beam in the second cell (i.e., DU 20) based on PRACH configuration information identified for the second cell (i.e., a target cell of a current handover) and information on the specific beam identified in the measurement report MR of the UE1 (i.e., the specific beam of the DU 20).

In this case, the predicted specific time may be a PRACH slot position to which a resource allocated to a specific beam identified from the PRACH configuration information of the DU20 and a RACH Occasion (RO) previously allocated to the UE1 are mapped.

For example, if PRACH configuration information of the target cell (i.e., DU 20) is identified, the time determination unit 220 may identify the structure of PRACH slots in which RX beam scanning is performed in units of PRACH slots (PRACH #1, #2, … # n) in the DU20, a beam mapping rule, and an RACH period.

Accordingly, if the UE1 identifies information (e.g., SSB index) on a specific beam of the DU20 having the best signal quality, the time determination unit 220 may identify a PRACH slot during which the DU20 within the RACH period can receive a random access preamble through the specific beam.

In this case, the time determination unit 220 may predict the time of the access attempt, i.e., the time of receiving the random access preamble from the UE1 (that is, a PRACH slot position mapped to a RACH Occasion (RO) previously allocated to the UE1 among PRACH slots during which the DU20 can receive the random access preamble through a specific beam within the RACH period) as a specific time S _ 1.

In addition, the time determination unit 220 may determine the transmission time based on the specific time S _1 predicted as described above.

According to an embodiment, the time determination unit 220 may also determine the specific time S _1 predicted as described above as the transmission time.

According to a more detailed embodiment, in addition to predicting the specific time S _1 as described above, when receiving the specific message (i.e., the RRC connection reconfiguration message), the time determination unit 220 may predict a processing time S _2 required to process the RRC connection reconfiguration message and transmit the random access preamble message to the target cell (i.e., DU 20) based on the capability information of the UE 1.

The CU 100 may possess capability information of the UE through UE capability information transmitted from the UE in a connection process with a new UE.

Accordingly, since the time determination unit 220 can recognize the performance information of the UE1 from the CU 100, the time determination unit 220 can predict the processing time S _2 of the UE1 based thereon.

Accordingly, the time determination unit 220 may determine a time earlier than the specific time S _1 predicted as described above by the processing time S _2 of the UE1 predicted as described above as the transmission time.

The message transmission unit 230 waits for the transmission CU 100 to transmit the RRC connection reconfiguration message generated for the UE1 until the transmission time determined by predicting the specific time S _1 and the processing time S _2 in the time determination unit 220, and then transmits the RRC connection reconfiguration message to the UE 1.

Fig. 4 illustrates an example of applying a cell access control scheme according to an embodiment of the present disclosure to a MIMO communication system.

Referring to fig. 4, UE1 may use a data service through CU 100 based on a source cell (i.e., a cell of source DU 10).

Further, in the MIMO communication system, the respective DUs (e.g., 10 and 20) perform TX beam scanning for transmitting a specific signal (e.g., SSB, CSI-RS, etc.) including a beam identifier for each of the plurality of beams formed therein based on a beamforming technique.

Fig. 4 shows that each of

DUs

10 and 20 performs TX beam scanning (r) for transmitting an SSB signal (SSB #1, #2, … # n) including a beam identifier (e.g., SSB index) for each of a plurality of beams formed therein.

In addition, the UE1 measures a received specific signal (e.g., SSB, CSI-RS, etc.) and transmits a measurement report MR (c) for reporting signal qualities (e.g., SINR, RSRP, PSRQ, etc.) of respective beams of neighboring cells.

The CU 100 receives the measurement report MR of the UE1, and if there is a neighboring cell (e.g., DU 20) having a signal quality equal to or higher by a certain value than that of the source DU 10 based on the measurement report (a3 event), determines handover such that the corresponding DU20 becomes a target cell of the UE 1. In addition, the CU 100 can perform the handover preparation procedure ((c)) with the target DU by signaling (target cell AU establishment request and target cell AU establishment response).

After performing the handover preparation procedure, the CU 100 generates an RRC connection reconfiguration message to transmit the access procedure based on the target DU to the UE1, determines a transmission time based on the specific time S _1 and the processing time S _2 predicted as described above, and waits for the transmission of the RRC connection reconfiguration message until the transmission time (S1).

The UE1 may continue the data transmission operation based on the source DU 10 while waiting to transmit the RRC connection reconfiguration message generated to be transmitted to the UE 1.

Further, the target DU20 may allocate a plurality of beams to each cell resource in each PRACH slot according to a beam mapping rule based on the PRACH configuration defined therein, and may perform RX beam scanning in units of PRACH slots (PRACH #1, #2, … # n).

At the transmission time, the CU 100 transmits the RRC connection reconfiguration message waiting for transmission to the UE1 (S2).

In this case, since the transmission time is determined based on the time of receiving the random access preamble from the UE1, i.e., the specific time S _1 mapped to the RACH Occasion (RO) previously allocated to the UE1, which is predicted as the location of the PRACH slot of the target DU20, in step S1, the transmission time may be a time immediately before the RACH Occasion (RO) of the UE1, or may be an earlier but very close time.

Further, although it is illustrated in fig. 4 that the CU 100 waits for the transmission of the RRC connection reconfiguration message, the CU 100 may transmit the RRC connection reconfiguration message to the source DU 10 when generating it, and the source DU 10 may wait for the transmission of the RRC connection reconfiguration message.

In this case, at the transmission time, the source DU 10 transmits the RRC connection reconfiguration message waiting for transmission to the UE 1.

Accordingly, the UE1 receiving the RRC connection reconfiguration message may stop the data transmission operation based on the source DU 10 and, after a while, may transmit a random access preamble in the RO assigned thereto (sixth) to start a random access procedure attempting to access the target DU20, thereby performing the access procedure based on the target DU 20.

The target DU20 may receive a random access preamble in a PRACH slot (e.g., PRACH # j) mapped to the RO of the UE1 while performing RX beam scanning in units of PRACH slots (PRACH #1, #2, … # n), may transmit a random access response thereto (c), and may perform a random access procedure through a series of signaling operations.

Thereafter, an access procedure based on the target DU20 may be performed through a series of signaling operations between the UE1, the target DU20, and the CU 100, and if the UE1 transmits an RRC reconfiguration complete message to the CU 100 through the target DU20, the access procedure may be completed so that the UE1 can use a data service through the CU 100 based on the cell of the target DU 20.

UE1 has a data interruption time (c) from when the RRC connection reconfiguration message is received to when the data transmission operation is interrupted when the target cell-based access procedure is completed by transmitting the RRC reconfiguration complete message.

As shown in fig. 4, according to the embodiment of the present disclosure, the data interruption time in the UE1 is reduced by the time T compared to the related art in which the RRC connection reconfiguration message is transmitted immediately after the message is generated₁。

As described above, according to the embodiments of the present disclosure, a cell access control scheme is implemented such that a transmission time of an RRC connection reconfiguration message transmitted to a UE is adjusted (maintained) in consideration of a large amount of time required to receive a random access preamble (random access procedure start signal) of the UE through RX beam scanning of a cell when a connection is made between the UE and the cell (e.g., a target cell) in a MIMO system.

Further, according to a more detailed embodiment, if a specific event (e.g., an a2 event) in which the signal quality of the first cell, i.e., the source cell (e.g., the cell of DU 10) becomes lower than a threshold value is reported from UE1 while waiting for a specific message (i.e., an RRC connection reconfiguration message) to be transmitted, message transmission unit 230 may immediately transmit the RRC connection reconfiguration message to UE1 regardless of the transmission time determined by time determination unit 220.

In case that the channel environment between the UE1 and the source cell (e.g., the cell of the DU 10) rapidly deteriorates, the a2 event is reported/generated.

In the case where the channel environment between the UE1 and the source cell (e.g., the cell of DU 10) rapidly deteriorates as described above, if the RRC connection reconfiguration message waits to be transmitted and then is transmitted at the transmission time, the message cannot be normally transmitted to the UE1 and the access procedure cannot be normally performed.

Therefore, in the present disclosure, if an a2 event indicating that the channel environment between UE1 and the source cell (e.g., the cell of DU 10) is rapidly deteriorating is reported from UE1 even while waiting for the RRC connection reconfiguration message to be transmitted, the RRC connection reconfiguration message may be immediately transmitted to UE1 regardless of the transmission time so that the message may be normally transmitted to UE 1.

Fig. 5 illustrates an example of applying a cell access control scheme according to another embodiment of the present disclosure to a MIMO system.

For simplicity of explanation, descriptions of SSB signal scanning ((r)), transmission of measurement report MR of UE1 ((r)), execution of handover preparation procedure ((c)), determination of transmission time for RRC connection reconfiguration message, and waiting for transmission (S1), which have been described with respect to fig. 4, will be omitted.

UE1 continues the data transmission operation based on the source DU 10 while waiting for the transmission of the RRC connection reconfiguration message generated to be transmitted to UE 1.

Further, the target DU20 allocates a plurality of beams to each cell resource in each PRACH slot according to a beam mapping rule based on the PRACH configuration defined therein, and may perform RX beam scanning in units of PRACH slots (PRACH #1, #2, … # n).

Further, the UE1 repeats the operation of measuring each received specific signal (e.g., SSB, CSI-RS, etc.) and transmitting a measurement report MR indicating the signal quality of each beam of the neighboring cell (S3).

If an a2 event report indicating that the signal quality of the source DU 10 is below the threshold is identified based on the measurement report, the CU 100 receiving the measurement report MR of the UE1 immediately transmits an RRC connection reconfiguration message waiting for transmission to the UE1 even before the transmission time (S4).

In this case, the transmission time in step S4 may be earlier than the transmission time determined in step S1.

Accordingly, the UE1 receiving the RRC connection reconfiguration message may stop the data transmission operation based on the source DU 10 and may transmit a random access preamble in the RO allocated thereto (sixth) to start a random access procedure attempting to access the target DU20, thereby performing the access procedure based on the target DU 20.

As shown in fig. 5, according to the embodiment of the present disclosure, the data interruption time in the UE1 is reduced by the time T compared to the related art in which the RRC connection reconfiguration message is transmitted immediately after the message is generated₂(<T₁)。

Therefore, according to the embodiments of the present disclosure, since the data interruption time of the UE side can be reduced by the adjustment amount up to the transmission time of the RRC connection reconfiguration message, an effect of minimizing the data interruption time can be provided.

In particular, according to the embodiments of the present disclosure, when the transmission time of the RRC connection reconfiguration message transmitted to the UE is adjusted, the processing time S _2 depending on the performance of the UE is reflected, thereby obtaining an effect that the normal access procedure can be performed while minimizing the data interruption time on the UE side.

In addition, according to the embodiments of the present disclosure, if the channel environment between the UE and the source cell rapidly deteriorates while maintaining the transmission time of the RRC connection reconfiguration message transmitted to the UE, the RRC connection reconfiguration message is immediately transmitted, thereby obtaining an effect that the normal access procedure can be performed while minimizing the data interruption time on the UE side.

Hereinafter, a cell access control method according to an embodiment of the present disclosure will be described with reference to fig. 6.

According to the cell access control method according to the embodiment of the present disclosure, the cell access control device 200 may learn information (e.g., SSB information and PRACH configuration information) of each cell by sharing information between cells or by having information of a corresponding cell (S100).

Hereinafter, for convenience of description, description will be made assuming that handover of the UE is performed.

According to the cell access control method according to the embodiment of the present disclosure, the cell access control device 200 (or the CU 100) determines whether an a3 event indicating that there is a neighbor cell having a signal quality equal to or higher than the signal quality of the source cell (e.g., DU 10) of the UE based on the measurement report MR received from the UE occurs (S110).

According to the cell access control method according to the embodiment of the present disclosure, if it is determined that the A3 event occurs with respect to the UE1 (yes in S110), the cell access control device 200 (or the CU 100) determines handover with respect to the UE1 and determines a target cell for which handover is performed based on the measurement report MR (S120).

On the other hand, if the A3 event does not occur for the UE1 (no in S110), or if it is impossible to determine a target cell for which handover is to be performed even when the A3 event occurs (no in S120), the cell access control apparatus 200 (or CU 100) may not initiate handover of the UE1, and the UE1 may maintain data transmission based on the source cell (i.e., DU 10) (S115).

According to the cell access control method according to an embodiment of the present disclosure, if a target cell (e.g., DU 20) for handover is determined (yes in S120), the cell access control device 200 may predict a specific time at which an access attempt is received from the UE1 through a specific beam in the second cell (i.e., DU 20) based on PRACH configuration information identified for the target cell (i.e., DU 20) and information on the specific beam identified in the measurement report MR of the UE1 (i.e., the specific beam of the DU 20) (S130).

For example, if PRACH configuration information of the target cell (i.e., DU 20) is identified, the cell access control device 200 may identify the structure of PRACH slots in which RX beam scanning is performed in units of PRACH slots (PRACH #1, #2, … # n) in the DU20, an RACH period, and a beam mapping rule.

Accordingly, if the UE1 recognizes information (e.g., SSB index) on a specific beam of the DU20 having the best signal quality, the cell access control device 200 may recognize the PRACH slot in which the DU20 within the RACH period can receive the random access preamble through the specific beam.

In this case, the cell access control device 200 may predict the time of the access attempt, i.e., the time of receiving the random access preamble from the UE1 (that is, a PRACH slot position mapped to a RACH Occasion (RO) previously allocated to the UE1 among PRACH slots during which the random access preamble is received through a specific beam) as a specific time S _1 within the RACH period.

In addition, according to the cell access control method according to the embodiment of the present disclosure, when receiving the RRC connection reconfiguration message, the cell access control device 200 may predict a processing time S _2 required to process the RRC connection reconfiguration message and transmit the random access preamble message to the target cell (i.e., DU 20) based on the capability information of the UE1 (S140).

Therefore, since the cell access control device 200 can recognize the performance information of the UE1 from the CU 100, the cell access control device 200 can predict the processing time S _2 of the UE1 based thereon.

According to the cell access control method according to the embodiment of the present disclosure, the cell access control device 200 may determine as the transmission time (S _1-S _2) (S150) a time earlier than the specific time S _1 predicted in step S130 as described above by the processing time S _2 of the UE1 predicted in step S140 as described above.

According to the cell access control method according to the embodiment of the present disclosure, the cell access control device 200 waits for the RRC connection reconfiguration message generated by the CU 100 immediately after step S120 of determining the target cell (e.g., DU 20) for handover to be transmitted to the UE1 until the transmission time determined in step S150, and then transmits the message to the UE1 thereafter (yes in S160 and S170).

The UE may maintain the data transmission based on the source cell (i.e., DU 10) while the cell access control device 200 waits for the transmission of the generated RRC connection reconfiguration message to be transmitted to the UE1 (S190).

Further, according to the cell access control method according to the embodiment of the present disclosure, if it is determined that the a2 event has occurred even before the transmission time determined in step S150 (no in S160) to indicate that the channel environment between the UE1 and the source cell (i.e., the cell of DU 10) is rapidly deteriorated (yes in S180), the cell access control device 200 immediately transmits the RRC connection reconfiguration message to the UE1 regardless of the transmission time (S170).

Then, the UE1 receiving the RRC connection reconfiguration message may stop the data transmission operation based on the source cell (i.e., DU 10) and, after a while, may transmit a random access preamble in the RO assigned thereto to start a random access procedure attempting to access the target cell (i.e., DU 20), thereby performing an access procedure based on the target DU 20.

Thereafter, an access procedure based on the target DU20 may be performed through a series of signaling operations between the UE1, the target cell (i.e., DU 20), and the CU 100, and if the UE1 transmits an RRC reconfiguration complete message to the CU 100 through the DU20, the access procedure may be completed so that the UE1 can use a data service through the CU 100 based on the cell of the DU 20.

As described above, according to the embodiments of the present disclosure, a new cell access control scheme can be implemented by adjusting the transmission time of an RRC connection reconfiguration message to an optimal time that can minimize a data interruption time on the UE side when a connection is made between a UE and a cell (e.g., a target cell) in a MIMO system.

Therefore, according to the embodiments of the present disclosure, it is possible to provide an effect of minimizing a data interruption time on a UE side while enabling a normal access procedure to be performed when a connection is made between a UE and a cell (e.g., a target cell) in a MIMO system.

The cell access control method according to an embodiment of the present disclosure may be implemented in the form of program commands executed by various computer devices, and may be recorded in a computer-readable medium. The computer readable medium may include program commands, data files, data structures, or a combination thereof. The program commands recorded on the medium may be specially designed and configured for the present disclosure, or may be known and available to those skilled in the computer software art. Examples of the computer readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, magneto-optical media such as optical floppy disks, and hardware devices such as ROMs, RAMs, flash memories, and the like that are specially configured to store and execute program instructions. Examples of the program command include a high-level language code that can be executed by a computer using an interpreter or the like and a machine language code such as a machine language code generated by a compiler. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present disclosure, and vice versa.

Although the present disclosure has been described in detail with reference to the above various embodiments, the present disclosure is not limited to the above embodiments, and it should be understood that the technical spirit of the present disclosure extends to the scope in which any person skilled in the art to which the present disclosure pertains may make various changes or modifications without departing from the scope of the present disclosure as claimed in the appended claims.

Claims

1. An apparatus for controlling access to a cell, the apparatus comprising:

a cell checking unit configured to identify a second cell to which a user equipment, UE, accessing a first cell is to access based on a measurement report received from the UE;

a time determination unit configured to determine a transmission time of a specific message for inducing an attempt to access the second cell; and

a message transmitting unit configured to delay transmission of the specific message to the UE when the specific message is generated, and transmit the specific message at the determined transmission time.

2. The apparatus of claim 1, wherein the specific message is an RRC connection reconfiguration message that causes the UE to cease data transmission operations based on the first cell and attempt to access the second cell to perform an access procedure.

3. The apparatus according to claim 1, wherein the measurement report includes information on a specific beam having the best signal quality measured by the UE among a plurality of beams formed in different directions in the second cell, and

wherein the time determination unit is configured to determine the transmission time based on physical random access channel, PRACH, configuration information identified for the second cell and information about the particular beam.

4. The apparatus of claim 3, wherein the time determination unit is configured to:

predicting a particular time to receive an attempt from the UE to access the second cell over the particular beam based on the PRACH configuration information and the information about the particular beam; and

determining the transmission time based on the predicted specific time.

5. The apparatus of claim 4, wherein the particular time predicted is a PRACH slot location to which a resource allocated to the particular beam and a RACH Occasion (RO) allocated to the UE identified from the PRACH configuration information are mapped.

6. The apparatus of claim 4, wherein the time determination unit is configured to:

predicting a processing time required to process the specific message upon receipt of the specific message, and transmitting a message for attempting to access the second cell based on performance information of the UE; and

determining a time that is earlier than the predicted specific time by the processing time as the transmission time.

7. The apparatus according to claim 1, wherein the message transmitting unit is configured to transmit the specific message immediately regardless of the transmission time when a specific event that the signal quality of the first cell is lower than a threshold is reported from the UE while the specific message is transmitted later.

8. A method for controlling access to a cell in a base station, wherein the method comprises the steps of:

identifying a second cell to be accessed by a User Equipment (UE) accessing a first cell based on a measurement report received from the UE;

determining a transmission time of a specific message for inducing an attempt to access the second cell; and

when the specific message is generated, delaying to send the specific message to the UE, and sending the specific message at the determined sending time.

9. The method according to claim 8, wherein the measurement report includes information on a specific beam having the best signal quality measured by the UE among a plurality of beams formed in different directions in the second cell, and

wherein the determining comprises determining the transmission time based on physical random access channel, PRACH, configuration information identified for the second cell and information about the particular beam.

10. The method of claim 9, wherein the determining comprises:

determining the transmission time based on the predicted specific time.

11. The method of claim 10, wherein the particular time predicted is a PRACH slot location to which a resource allocated to the particular beam and a RACH occasion RO allocated to the UE identified from the PRACH configuration information are mapped.

12. The method of claim 10, wherein the determining comprises:

13. The method of claim 8, wherein the sending comprises sending the particular message immediately regardless of the sending time when a particular event is reported from the UE that a signal quality of the first cell is below a threshold while delaying sending the particular message.